System and method for treating liquids

ABSTRACT

A system for treating wastewater includes a basin to contain wastewater, an aerator provided in the basin to mix the wastewater, and a cover system to cover a surface of the wastewater contained in the basin. The cover system includes a plurality of hollow bodies disposed on the surface of the wastewater. Each hollow body is adapted to float on the wastewater&#39;s surface, and has a contiguous outer surface and a sufficient mass so that 30 to 70 percent of the hollow body&#39;s outer surface is exposed to atmosphere during use. A method of treating wastewater is further disclosed.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/225,385, entitled “SYSTEM AND METHOD FOR TREATINGWASTEWATER,” filed on Sep. 13, 2005, which claims benefit of U.S.Provisional Application Ser. No. 60/609,423, entitled “SYSTEM AND METHODFOR TREATING WASTEWATER,” filed on Sep. 13, 2004, both of which areherein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems and methods fortreating liquids, such as wastewater, and more particularly to awastewater treatment system and method capable of treating and coveringwastewater contained in a treatment basin.

2. Discussion of Related Art

In liquid treatment facilities, such as a wastewater treatment facility,it is well known to provide an aerator or a mixer to stimulatewastewater contained in a treatment basin. Mixers provide desired mixingof the wastewater so as to stimulate biological material used to treatthe wastewater. Aerators also mix the wastewater and provide the addedfeature of introducing oxygen into the wastewater. For the purposes ofthis disclosure, the term “aerator” will be used to describe bothaerators and mixers, and other types of aeration devices, such asaspirating aerators, unless otherwise described separately. In suchfacilities, it is further well known to cover the wastewater basin toprevent birds from nesting in the wastewater basin, to reduce heat loss,to reduce odors emanating from the basin, and to control the growth ofalgae within the basin by reducing sunlight.

One issue in designing a cover is that the cover must be compatible withthe aerator, which can be designed to float on the water's surface.Surface aerators have several advantages over submerged aerators, suchas lower installed cost, quick and simple installation, and virtually noroutine maintenance requirements. One disadvantage with such surfaceaerators is that cooling caused by operating in winter conditions, forexample, can reduce the biological treatment efficiency. Anotherdisadvantage is that surface aerators are often used in lagoon treatmentprocesses having a large surface area, which can result in a longhydraulic retention time. This long retention time can lead to algaeblooms, which in turn can lead to effluent TSS, BOD₅, and turbidity.Thus, it is somewhat important to control or eliminate algae to optimizethe overall treatment performance of the wastewater treatment system.

There is presently available a fiberglass cover that is an optionalattachment for surface aerators to reduce heat loss as well as tocontrol excessive misting and odors caused by the aerator spray.Specifically, this type of cover serves as a dome provided directly overthe surface aerator to control mist and water flow resulting from theaerator water discharge. Such a cover, while effective in controllingthe mist, is less effective in reducing heat loss in a basin having along retention time. In addition, a domed cover does not provide algaecontrol, nor does it prevent birds from nesting in the basin.

There are also commercially available polyester fabric covers that areeffective in shading the surface. One disadvantage associated with suchfabric covers is that the seams, which attach the fabric sheets to oneanother, are susceptible to degradation. Another disadvantage is thatadequate space must be provided around the aerator to prevent the fabriccover from being ingested by the aerator during its operation.

Another water surface “cover” is provided in the form of hollow plasticballs that cover 90% of the water's surface. In one known application,each ball is fabricated from black, ultra violet-stabilized, highdensity polyethylene. The ball is 100 millimeters (four inches) indiameter, has a wall thickness of less than 1 mm, and weighs 40 grams.Each ball can be formed with an opening that is closed by a plug. Thisconstruction enables the ball to be filled with water for ballast andthereby prevent the ball from being blown out of the basin during windyconditions. One problem associated with this construction is that theballs, due to the susceptibility of the plugs becoming dislodged, willleak over time. This results in the sinking of the balls, and theinevitable result of being ingested by the aerator, thereby causing indamage to the aerator. Balls formed without a plug are extremely lightand subject to being blown out of the basin.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to a system for treating liquidscomprising a basin to contain liquid, and a cover system to cover asurface of the liquid contained in the basin. The cover system comprisesa plurality of hollow bodies disposed on the surface of the liquid. Eachhollow body is adapted to float on the liquid's surface, and has acontiguous outer surface and a sufficient mass so that 30 to 70 percentof the hollow body's outer surface is exposed to atmosphere during use.

The hollow body has a wall with a thickness between 1 mm and 15 mm, andis spherical in shape. In one embodiment, the hollow body has a diameterof about 100 mm and a mass between 40 grams and 300 grams, andpreferably a mass between 200 grams and 240 grams. The hollow body isfabricated from polyethylene, which has a density of 0.948 gm/cm³.

The system may further comprise an aerator provided in the basin to mixthe liquid. In one embodiment, the liquid is wastewater.

Another aspect of the invention is directed to a method of treatingwastewater comprising: (a) depositing wastewater within a wastewatertreatment basin; (b) treating the wastewater with a biologically activematerial; and (c) covering a surface of the wastewater with a pluralityof hollow bodies disposed on the surface of the wastewater. Each hollowbody is adapted to float on the wastewater's surface, and has acontiguous outer surface and a sufficient mass so that 30 to 70 percentof the hollow body's outer surface is exposed to atmosphere during use.The method may further comprise mixing the wastewater with an apparatusdisposed within the basin.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the figures which are incorporated herein by reference and in which:

FIG. 1 is a perspective view illustrating a system for treating liquids,such as wastewater, in accordance with one embodiment of the presentinvention;

FIG. 2 is a perspective view illustrating the system of FIG. 1, with anaerator of the system operating to spray and mix liquids;

FIG. 3 is an elevational view showing an aerator in accordance with anembodiment of the present invention;

FIG. 4 is an elevational view showing a mixer in accordance with anembodiment of the present invention;

FIG. 5 is an enlarged, partial cross-sectional view of a hollow sphereused in the system for treating liquids in accordance with an embodimentof the present invention; and

FIG. 6 is a flow diagram showing a method of treating liquids inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

One embodiment of the present invention is directed to a liquidtreatment system and, more particularly, to a cover system employing aplurality of hollow spheres used to cover liquid, such as wastewater,during treatment. In such a treatment system, liquid, such aswastewater, is delivered to a space designed to contain the liquid. Inone embodiment, the space is a basin or lagoon, for example, which isdesigned to contain liquid without any seepage into the environment. Thebasin may embody a naturally existing configuration, a man-madestructure, or a combination of both, which is designed to containliquid. It should be understood that the basin may embody any structuredesigned to contain liquid and still fall within the scope of thepresent invention.

In such a wastewater treatment system, an aerobic biological treatmentsystem uses biomass to digest or degrade biodegradable materials in theinfluent stream. In operation, the treatment system typicallydecontaminates the influent contained within a wastewater treatmentbasin in a treatment cycle composed of a series of steps or periods.These treatment steps may vary according to a number of factorsincluding, for example, influent flow rate, pollutant concentration andtype, biomass concentration and diversity or type, ambient temperature,air flow, and other conditions, such as downstream capacity andavailability.

The various embodiments and aspects of the invention will be betterunderstood from the following definitions. As used herein, “influent”defines a stream of “wastewater” or “water,” from a municipal orindustrial source, having pollutants or “biodegradable material,”inorganic or organic compounds capable of being decomposed by bacteria,flowing into the wastewater treatment system. A “wastewater treatmentapparatus” is a system, typically a biological treatment system, havinga “biomass,” a population of bacterial micro-organisms or a diversity oftypes of bacteria, used to digest biodegradable material. Notably, thebiomass requires an environment that provides the proper conditions forgrowth including nutrients. It should be understood that the coversystem disclosed herein may be employed in any type of system designedto treat a liquid, and the term “wastewater” is used to designate anytype of liquid requiring treatment.

“Digestion” refers to the biodegradation process where the biomassconsumes the biodegradable material and reduces the biodegradablematerial to solid material which can be flocculated and removed bygravity sedimentation or settling into sludge. For example, in thebiodegradation process, bacteria may use enzymes to hydrolyze orbreakdown complex organic compounds, such as carbohydrates, into simpleorganic molecules, like carbon dioxide and water. During digestion, thebacteria may also reproduce, which results in additional biomass. Thesettling process may also produce a substantially clear liquid layerabove the settled sludge layer. Notably, the sludge may contain digestedinorganic and organic materials and biomass.

Moreover, digestion may be under aerobic conditions wherein the biomassand the wastewater liquid mixes with oxygen. Alternatively, digestionmay be under “anoxic” or anaerobic conditions, where no oxygen or air isadded to the reaction. The latter is used to facilitate biodegradationof nitrogen containing compounds, such as nitrates.

Turning now to the drawings, and more particularly to FIGS. 1 and 2,there is generally indicated at 10 a system of at least one embodimentof the present invention for treating wastewater. As shown, wastewateris contained within a basin or lagoon, which is designed to contain thewastewater without any seepage of the wastewater into the environment.Provided within the basin is an aerator, generally indicated at 12,which floats on the surface of the wastewater. As will be describedbelow, the aerator 12, depending upon whether it is a mixer or anaerator, stimulates the movement of the wastewater within the basin. Theaerator 12 is held in place within the basin by cables, each indicatedat 14. Other devices, such as posts, can be employed to hold the aerator12 in place. The system 10 further includes a cover system generallyindicated at 16, in accordance with an embodiment of the presentinvention, to cover the surface of the wastewater.

Referring to FIGS. 2 and 3, the aerator 12 can be chosen from any of thewell-known aerators. For example, the aerator may be of the type thatmixes and sprays wastewater to introduce oxygen into the wastewater.This type of aerator 12 is illustrated in FIG. 3 and is offered by U.S.Filter Aerator Products of Roscoe, Ill., the assignee of the presentinvention, under the brand name AQUA-LATOR®. As shown in FIG. 2, duringoperation, the aerator 12 sprays wastewater into atmosphere forpositively introducing oxygen into the wastewater.

Referring to FIG. 4, the aerator may alternatively be of the type thatonly mixes the wastewater underneath the surface of the wastewater. Thistype of aerator 12 is illustrated in FIG. 4 and is also offered by U.S.Filter Aerator Products under the AQUA-LATOR® brand name. The mixer-typeaerator is incapable of spraying wastewater and therefore does notpositively introducing oxygen into the wastewater as with thesprayer-type aerator. The aerator may also be of the type that issubmerged.

Turning back to FIGS. 1 and 2, the cover system 16 includes a pluralityof hollow, spherically-shaped bodies or balls, each indicated at 18. Anysuitably shaped body can be chosen by the person of ordinary skill inthe art, given the benefit of this disclosure; however,spherically-shaped balls are easier to manufacture and operate moreefficiently, as will be described in detail below. The number of balls18 depends on the size of the surface area of the wastewater to betreated. The balls 18 are adapted to float on the wastewater's surfaceso as to provide a uniform layer across the surface of the wastewater.This configuration reduces the penetration of sunlight by approximately90%, which significantly reduces the photosynthesis of algae. Duringoperation of the aerator (FIG. 2), the balls 18 are pushed away from theaerator 12 and stacked up by the spray of the aerator 12.

With reference to FIG. 5, each ball 18 is formed with a contiguous outersurface 20 having no openings provided therein as with the prior artballs described above. Preferably, the ball 18 is fabricated from asuitable polymeric material, such as black, ultra violate-stabilizedpolyethylene. The density of the polyethylene depends on the massrequirement of the ball. For example, for lighter balls, a high densitypolyethylene (HDPE) is used due to a relatively thin wall thickness.More particularly, a thin walled ball requires a higher strengthmaterial to withstand environmental elements. Conversely, heavier ballswould require a medium density polyethylene with a greater wallthickness, as will be described in greater detail below. Other materialscan also be used and are dependent on the specific application. Theweight of the ball 18 can vary according to application requirements.For example, heavier balls may be required for use near airports toprevent the balls from being blown out of the basin by jet aircraftexhaust or strong winds.

Each ball 18 is approximately 100 millimeters (mm) in diameter, and isfabricated from any suitable process, such as an injection mold process.It should be understood that a person of ordinary skill in the art,given the benefit of this disclosure, could employ a ball having adifferent diameter. Preferably, the ball can be between 25 mm and 150 mmin diameter. The body of the ball 18 is defined by a wall 22, which hasa thickness between approximately 1 mm and 15 mm, preferably a thicknessbetween 7 mm and 10 mm, and most preferably a thickness of about 8.74mm. A wall thickness of 8.74 mm provides sufficient mass so that 30 to70 percent of the ball's outer surface 20 is exposed to atmosphere abovethe surface of the wastewater during use as illustrated in FIG. 5.Preferably, 40 to 60 percent of the balls outer surface is exposed, andmost preferably 50 to 60 percent of the ball's outer surface is exposed.The preferred material, medium density polyethylene, has a density of0.948 grams/centimeter³ (gm/cm³). Thus, for a ball having a wallthickness of 8.74 mm, the mass of the ball is approximately 220 grams.It should be understood, however, that a ball having a mass between 40and 300 grams, and preferably between 200 and 240 grams, is contemplatedherein so long as the ball retains a portion of its outer surface in thewastewater.

It should be noted that in one embodiment the ball 18 disclosed hereinhas a contiguous outer surface without an opening and plug as requiredby the prior art plastic ball described above. The thick wallconstruction of the ball 18 provides the necessary ballast so as to restfirmly within the wastewater during use. And, since the ball 18 does nothave an opening and plug, it is not susceptible to sinking. Moreover,the air inside the ball 18 and the low thermal conductivity of thepolyethylene provide a thermal insulation barrier that reduces heat lossfrom the wastewater.

Furthermore, the cover system 16 does not restrict the installation andmovement of the floating aerator 12, and allows normal access of thesurface of the wastewater for routine sampling. The balls 18 are adaptedto rise and fall with changes in the wastewater level, and maintaincomplete surface coverage at all levels. Specifically, as the wastewaterlevel drops, the balls automatically stack up into two or more layers,and then re-cover the surface in a single layer as the water rises. Theincreased surface area associated with sloped basins is accommodated byadding a sufficient quantity of balls to cover the wastewater surface atthe maximum level.

In another aspect of the present invention, the system 10 includingaerator 12 and cover system 16 are used to provide biological treatmentof an airport de-icing runoff basin and, at the same time, prevent birdsfrom nesting near the runoff basin by creating an illusion of a solidsurface over the entire surface of the water. This application of thepresent invention is considered a viable wildlife control technique toassist in preventing the potentially catastrophic effect of a birdentering an aircraft's jet engine.

Referring to FIG. 6, in another aspect of the instant invention, amethod of treating wastewater, generally indicated at 30, is furtherdisclosed. In one embodiment, the method comprises: (a) depositingwastewater within a wastewater treatment basin at 32; (b) treating thewastewater with a biologically active material at 34; (c) mixing thewastewater with an apparatus (e.g., aerator 12) disposed within thebasin at 36; and (d) covering a surface of the wastewater with aplurality of hollow bodies (e.g., balls 18) disposed on the surface ofthe wastewater at 38. The hollow balls 18 are simply deposited into thebasin wherein the wastewater flow generated by the aerator 12 allows theballs to settle in a uniform layer that covers the entire surface of thewastewater, provided a sufficient number of balls is deposited. Theballs 18 are pushed away and stacked up by the spray generated by theaerator 12 such that the aeration efficiency and mixing performance arenot negatively affected. When the aerator 12 is turned off, the balls 18automatically re-cover the entire water surface provided a sufficientamount of balls is provided in the basin.

It should be understood that the teachings of the present inventioncould be applied to other related applications, such as storm watercollection ponds and to any other open water basin applications.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1.-18. (canceled)
 19. A method of treating wastewater comprising:depositing wastewater within a wastewater treatment basin; treating thewastewater with a biologically active material; and covering a surfaceof the wastewater with a plurality of hollow bodies disposed on thesurface of the wastewater, each hollow body being adapted to float onthe wastewater's surface, each hollow body having a contiguous outersurface and a sufficient mass so that 30 to 70 percent of the hollowbody's outer surface is exposed to atmosphere during use.
 20. The methodof claim 19, further comprising mixing the wastewater with an apparatusdisposed within the basin.
 21. A method of treating wastewatercomprising: depositing wastewater within a wastewater treatment basin;treating the wastewater with a biologically active material; covering asurface of the wastewater with a plurality of hollow bodies disposed onthe surface of the wastewater, each hollow body being adapted to floaton the wastewater's surface; and mixing the wastewater with an apparatusdisposed within the basin.
 22. The method of claim 21, wherein eachhollow body has a wall with a thickness between 1 mm and 15 mm.
 23. Themethod of claim 21, wherein each hollow body is spherical in shape. 24.The method of claim 23, wherein each hollow body has a diameter of about100 mm.
 25. The method of claim 21, wherein each hollow body has a massbetween 40 grams and 300 grams.
 26. The method of claim 21, wherein eachhollow body has a mass between 200 grams and 240 grams.
 27. The methodof claim 21, wherein each hollow body is spherical in shape andfabricated from polyethylene, each hollow body having a mass between 40and 300 grams.
 28. The method of claim 27, wherein each hollow body hasa density of 0.948 gm/cm³.
 29. The method of claim 21, wherein theapparatus comprises a mixer provided in the basin to mix the wastewater.30. The method of claim 21, wherein the apparatus comprises an aeratorprovided in the basin to mix the wastewater.
 31. The method of claim 21,wherein the hollow body has a diameter between 25 mm and 150 mm.
 32. Themethod of claim 21, wherein each hollow body has a contiguous outersurface and a sufficient mass so that 30 to 70 percent of the hollowbody's outer surface is exposed to atmosphere during use.